Objective

Experimental details

1. Subjects Four male adult Thais 21 to 25 years old.
Their body weights were 45 to 67.5 kg, and their heights were 164.5 to 169 cm.
They were healthy and well-nourished, based on medical history, physical
examination, urinalysis, stool examination, chest x-ray, and a routine complete
blood count.

2. Study Environment The entire study was conducted at
the clinical research ward (a metabolic unit) in

Ramathibodi Hospital. The climatic characteristics were those of tropical
countries.

3. Physical Activity The subjects were allowed to
continue their usual activities but were not allowed to participate in
competitive, active sports.

4. Duration of the Study The study of obligatory
nitrogen losses was carried out over a 14-day period.

TABLE 1. Composition of the Protein-Free Diet

Ingredients

g/day

Mung bean
starch

100.4

Mung bean noodles

100.0

Sugar

1
08.6

Margarine

48.0

Oil

30.0

Onion leaf

30.0

Wax gourd

27.0

Salt

5.1

Lemon
juice

2.4

Soy sauce

2.0

Garlic

2.0

Carbonated beverage

variable

5. Diets The composition of the protein-free meal is
shown in table 1. The subjects were given four meals per day at 7.30 a.m., 12
noon, 5.00 p.m., and 9.30 p.m. Daily energy intakes were constant, at about 45
kcal/kg/day. Fat provided approximately 30 per cent of the daily energy intake.
Multivitamin and mineral tablets were given twice each day. Water was offered ad
libitum but the volume was recorded daily.

6. Indicators and Measurements

Total nitrogen in urine and faeces was measured by a calorimetric
semi-automated procedure (Munro and Fleck, Mammalian Protein Metabolism, vol. 3
[1969]). Nitrogen balance was calculated from the last five and ten days of
urinary and faecal nitrogen losses, respectively.

Serum concentrations of total
protein, albumin, urea nitrogen, and some amino acids and amino transferase
activities were measured at seven-day intervals.

TABLE 2. Obligatory Nitrogen Losses in Four Adult Thai Males

Subject

U

F

S

Total

M.P.

38.6

15.1

5

58.7

V.D.

32.5

12.4

5

49 9

S. R.

33.4

12.4

5

50.9

S.S.

35.0

10.6

5

50.6

Mean
± S.D.

34.9 ± 2.7

12.6 ± 1.9

5 ± 10

52.5 ± 4.2

U = urinary nitrogen losses, average from the last 5 days of 14-day dietary
period. F = faecal nitrogen losses, average from the last 10 days. S =
skin and other minor route nitrogen losses, taken from FAD/WHO.

Summary of main result

1. Daily Obligatory Nitrogen Losses in Four Adult Thai Males Table 2 shows the data for obligatory nitrogen losses of the subjects. The
means of urinary and faecal nitrogen losses were similar to most studies done in
other countries. Total obligatory nitrogen losses were calculated after allowing
5 mg N/kg/day for skin and other minor losses.

2. Plasma Amino Acids Table 3 shows that the
concentration of valine decreased, while concentrations of alanine and glycine
increased on days 7 and 14. The ratios of non-essential/essential amino acids
(NEA/EA ratio) and of glycine/valine increased.

3. Other Measurements Table 3 also shows that BMR and
blood urea nitrogen (BUN) were lower and ALT was higher by day 7. By day 14, all
indicators shown in the table differed from initial values.

TABLE 3. Blood Chemistry and Basal Metabolic Rates of Four Adult Thai Males
Eating a Protein-Free Diet for 14 Days

Protein-free diet

Measurement

Initial value

day 7

day 14

BMR (kcal/m²/day)

1,134 ± 94

927 ± 261*

906 ± 129*

Total protein
(g/dl)

7.5 ± 0.5

6.9 ± 0.9

6.9 ± 0.3*

Albumin
(g/dl)

5.3 ± 0.1

5.2± 0.3

4.8 ± 0.3*

BUN (mg/dl)

10.3 ± 3.1

3.3 ± 1.0*

2.7 ± 0.7*

AST (sigma
unit)

21.0 ± 3.4

24.0 ± 4.6

24.5 ± 3.8*

ALT (sigma
unit)

17.6 ± 0.9

23.3 ± 3.0*

24.0 ± 0.9*

Valine
(um/L)

258.5 ± 7.7

175.1 ± 30.8*

165.9 ± 18.6*

Alanine
(um/L)

219.8 ± 61.4

696.9 ± 225.4*

846.0 ± 153.8*

Glycine
(um/L)

299.7 ± 39.7

468.3 ± 15.0*

486.9 ± 31.8*

NEA/EA
ratio

2.2 ± 0.1

3.4 ± 0.5*

3.3 ± 0.5*

Gly/Val ratio

1.2 ± 0.1

2.7 ± 0.4*

3.0 ± 0.5*

* Differs from initial value p <
0.05.

Conclusions and comments

1. The results of obligatory nitrogen losses in this study of adult Thai
males were quite similar to those that have been reported on 4 Indian men, on 13
men studied at the University of California, on 9 Nigerian men, and in 83
studies on MIT students and 50 Chinese studies on males. It seems, therefore,
that the obligatory urinary and faecal nitrogen excretion of young men,
expressed as mg/kg/day, does not differ among ethnic groups.

2. Factorial calculation of safe levels of protein intake, using a correction
factor of 1.3 and adding another 30 per cent for individual variability, as
suggested in 1973 by FAO/WHO, results in 0.56 g/kg/day, which is almost
identical to the safe level of intake recommended by FAD/WHO. That
recommendation has recently been questioned for populations at large or for
long-term studies. Our own studies using multi-level nitrogen balance techniques
indicate that 0.56 9 protein/kg/day is too low (see Tontisirin et al., this
volume).

Acknowledgements

This study was supported by the research fund of the World Hunger Programme
of the United Nations University. We would like to thank Dr. V. Tanphaichitr for
medical care of the subjects, the staffs of the clinical research ward and food
analysis laboratory, Ramathibodi Hospital, for their assistance, and the
subjects who cooperated throughout the
study.